It is generally believed as difficult to arbitrarily control conductivity type of II-VI compound semiconductors having Zn (zinc) as a Group II element in the periodic table (Zn-base semiconductor) due to self-compensation effect caused by formation of intrinsic defect. Under such circumference of Zn-base semiconductor, a recent effort has been succeeded in obtaining an n-type ZnTe (zinc telluride), having Te (tellurium) as a group VI element in the periodic table, and having a small band gap energy which belongs to green wavelength band, and in fabricating a light emitting device based on homo-junction using ZnTe.
The above-described light emitting device based on homo-junction using ZnTe, however, suffers from a suppressed emission efficiency, because ZnTe intrinsically has p-type conductivity in its non-doped state, has a lower carrier concentration in the n-type layer than in the p-type layer, and carriers can uniformly diffuse in the vicinity of a p-n junction interface to be formed.
One possible way to raise the emission efficiency is such as forming a double heterostructure in which an active layer is typically composed of ZnTe, and cladding layers are composed of a Zn-base semiconductor containing ZnTe. Formation of the double heterostructure is generally proceeded by vapor phase epitaxy such as the epitaxial growth process, but formation of the double heterostructure using a ZnTe wafer as a substrate, for example, may raise production costs higher than that in the formation of a p-n junction interface based on homo-junction using the ZnTe wafer.
While not being limited for the cases of ZnTe, it is important subjects for any light emitting devices having a light emitting region composed of a Zn-base semiconductor, of which conductivity type is believed to be less controllable, to raise the emission efficiency based on an effective carrier injection into the light emitting region, and to raise the luminance of light to be extracted.
This invention was conceived taking the above-described subjects into consideration. In other words, it is therefore an object of this invention to provide a Zn-base semiconductor light emitting device which is possibly raised in the emission efficiency in a light emitting region composed of Zn-base semiconductor, and to provide a method of fabricating the same.